Aluminum flue liners are installed as a protective sleeve to keep moisture & carbon monoxide produced by gas appliances contained so that it can’t leach into concealed areas of the chimney or your home. This improves the performance of your appliances and the safety of a chimney. They can be in the form of individual rigid pieces or one continuous length of flexible tubing. These are available in multiple diameters from 3″ to 8″ and only round in shape as they are much more fragile than stainless steel. We supply & install these components.